The present invention relates to a program product, an image generation system, and an image generation method.
An image generation system (game system) which generates an image viewed from a virtual camera (given viewpoint) in an object space (virtual three-dimensional space) in which an object such as a character is positioned has been known. Such an image generation system is very popular as a system which enables experience of so-called virtual reality. In an image generation system which generates a game image for an action game in which a player causes a character to move in the object space or to show action by operating the character, a three-dimensional image is generated in which game production such as explosion, flame, or smoke is represented using an effect object when an event has occurred. A method of using an object which two-dimensionally represents an effect, such as a sprite polygon (billboard polygon), has been proposed for a system which generates such a three-dimensional image in order to simplify the processing (Japanese Patent Application No. 10-179932).
According to this method, if the effect object is positioned behind the virtual camera when an event (effect event) which causes the effect object to be generated has occurred near the player's character, a situation may occur in which the player cannot recognize the image effect to be seen. Even if the effect object is positioned in front of the virtual camera, a similar situation may also occur when the effect object is positioned between the virtual camera and the screen. In particular, when the effect object is provided with the effect of applying hit damage to the character operated by the player, an inconsistent situation may occur in which the player's character is damaged even though the player cannot recognize the image effect.